Air hardening graphitic steel



United States Patent ,0

AIR HARDENING GRAPHITIC STEEL No Drawing. Application December 6, 1957Serial No. 700,982

3 Claims. (Cl. 75-123) This invention relates to graphitic steels ofhigh hardenability and of controlled graphitic carbon content. The termhigh hardenability as used herein refers to the ability of the steel tobe hardened in still air from an austenitizing temperature to a minimumhardness of Rockwell C 58 (Re) throughout relatively heavy sections.

Graphitic steels are well known and they have been widely used. They arecharacterized by containing free graphite and they possess the abilityto develop high hardness, good machining properties, resistance to wear,and desirable mechanical properties. This combination of propertiesadapts those steels particularly for use as dies of a wide variety ofuses, and as punches, breaches, spinning rolls, and other tools forrelated uses.

Most of the known graphitic steels are hardened by liquid quenching. Anair hardening type has been proposed but experience has shown thatalthough it possesses good graphitizing properties it is not capable ofcommercial exploitation in sections greater than about 1 /2 inches. Incontrast, conventional air hardening steels, e.g., the standard SCr-lMo,the 12Cr-1.5C steels,

ability properties that characterize the invention and do not interferewith development of desired graphite levels brought about in the mannernow to be described. Thus, the steels may contain tungsten which, inprinciple, behaves similarly to molybdenum, as well as small amounts ofvanadium (up to 0.5 percent) which, in principle, behaves similarly tochromium and also acts as a grain refiner. p

In the practice of the invention the steels are melted, hot worked, andannealed to eflfect graphitization all in accordance with standardgraphitic steel practice, care being taken to avoid graphite formationin the ingots and during hot working. The steels should be hardened bycooling in air from within the range of about 1450" to 1550 F., thelower temperature being applicable to small sections, say up to one andone-half inch dimension, and the temperature being progressivelyincreased toward the upper value as the section size increases, e.g.,using 1525 F. at five and one-half inch and greater sections. These lowhardening temperatures are advantageous in that they are 200 to 300 F.below those necessary for most competitive non-graphitic air hardeningsteels. This confers low distortion, low decarburization, and lowretained austenite.

The annealed hardness, in which condition these steels are commonly soldto the trade, will normally range and some high manganese types, can beair hardened to Rc 60 at the centers of rounds as great as 4 inches, 5inches and 6 inches in diameter respectively.

It is among the objects of this invention to provide graphitic steelscapable of being hardened in air to a minimum of about Re 58, andpreferably of at least about Re 60, up to the center of sections aslarge as six-inch rounds and equivalent non-circular sections; that maybe produced and processed easily according to standard graphitic steelpractice; that possess good machinability; that gave dimensionalstability comparable to that of competitive non-graphitic steels; andthat may be hardened at comparatively low temperatures,

A further object is to provide steels in accordance with the foregoingobjects containing from about'0.2 to 0.6 percent of graphitic carbonthat is substantially uniformly dispersed throughout the section.

Other objects will be apparent from the following specification.

I have discovered, and it is upon this that the invention is largelypredicated, that the objects of the inven tion are attained with steelscontaining from about 1 to 2 percent of carbon, not over about 0.2percent of chromium, from about 1.7 to 2.5 percent of manganese, fromabout 1.3 to 1.75 percent of molybdenum, from about 1 to 2.5 percent ofnickel, and from about 1 to 1.5 percent of silicon. Preferably thesteels contain about 1.35 percent of carbon, less than about 0.15percent of chromium, about 1.85 percent of manganese, from about 1.4 to1.6 pcrcent of molybdenum, from about 1.8 to 1.9

The steels may contain phosphorus and sulfur in amounts found ingraphitic steels.

Apart from the foregoing alloying constituents, the

remainder of the steels is iron together withimpurities and elementsthat do not adversely afiect'the hardenv percent of nickel, and fromabout 1.15 to 1.25 percent 'of silicon.

from about 235 to 275 Brinell, according to the graphite level. Intempering, as to relieve stress or for rehardening, care should be takento keep the temperature below that at which re-solution occurs. p

These steels have good machinability. They machine with short,discontinuous chips characteristic of other graphitic steels. Theypossess excellent tempering characteristics.

As air hardened these new steels possess a microstructure ofspheroidized carbides uniformly distributed in a high strength matrixthrough Which there are also uniformly distributed particles ofgraphitic carbon. In general, with sections up to 3 inches the hardnessto be expected is 62-64 Rc, and with larger sections 60-63 Rc, whichhardness is substantially uniform across the section.-

The following examples are characteristic of the-steels of thisinvention. Each of them was made in a 40-ton electric furnace and theheats were poured into 20-inch square ingot molds to produce ingots of5150 pounds weight. The ingots were charged into a furnace at 1200 F.and cooled slowly to 200 F. after which they were reheated to 1925 F.and hot worked to shapes of various sections and sizes. The hot workedproducts were then given the following preliminary and final annealingcycles: a

e. in furnace at 10 Samples of the annealed stock having a length 2 /2times the diameter were turned from larger section sizes and hardened instill air. Analyses, graphitic carbon Patented Apr. 21, 1 959 contents,hardnesses and tempering data are given for each steel.

Example 1 This steel had the following analysis:

This heat was forged to 5", 5 /2", 7%, 8% and 9" rounds.

The annealed product showed the following graphite contents:

Section size- Graphite, percent 5" round .39 7%" round .42 8%" round .399" round .45

Hardening as described above gave the following results;

Re Hardness At- Surface Quarter Center 4" Bound Hardened From 1,475" F62. 8 62.0 61. 6 4 Round Hardened From 1.525 F 62. 5 62.0 61. 7 6" RoundHardened From 1,475 E. 61. 60. 0 59. 8 6" Round Hardened From 1,525 F-..61. 60. 3 60. 5

Two inch square samples were cut from a 7%" round in the as-annealedcondition. The two inch square samples were then hardened from 1450 F.and tempered for two hours at the temperatures indicated. The datafollow:

Example 2 This heat was likewise forged to produce various sizes ofrounds and squares. Its analysis was:

0 M11 P S Si Or N1 M0 The annealed product showed the following graphitecontents:

Section size-- Graphite, percent 6%" round .46 7" round .57 8" round .619" round .56 10 round .54 11" round .49 6" square .50 8" square .51

10" square .47

Hardening as described above gave the following results:

Re Hardness At- Surface Quarter Center 6" Round Hardened From 1,525 F.60.8 60.7 60. 8 7 Round Hardened From 1,525 F..." 58. 8 59. 5 58. 7

Two inch square samples were cut from a 7" round in the as-annealedcondition. The two inch square samples were then hardened from 1450 F.and tempered for two hours at temperatures indicated.

Tempering temperature, F.-- Rc hardness As-quenched 61.5 200 61.0 30061.0 400 59.5 500 59.0 600 58.0 700 -1 55.4 800 53.0 900 51.5 1000 46.01100 38.5 1200 32.5

Example 3 In this case the ingots were forged and rolled to producerounds and flats of varying sizes such as 4" and 6" forged rounds androlled flats varying from 1%" x 3" to 4" x 9". This heat had thefollowing analysis:

C Mn P 8 N1 M0 Typical graphite contents of the annealed products were:

Section size- 4" round 6" round .21

Hardening as described above gave the following results:

Graphite, percent .45

Re Hardness At;-

Surface Quarter Center 4" Round Hardened From 1,475 F 4" Round HardenedFrom 1,525 F 6" Round Hardened From 1.475 F 6 Round Hardened From 1,525F Two inch square samples were cut from a 6 inch square in theas-annealed condition. The two inch square samples were then hardenedfrom 1450 F. and tempered for two hours at temperatures indicated.

Tempering temperature, F.- Rc hardness As-quenched 62.0 200 63.0 30060.5 400 60.0 500 59.5 600 58.5 700 57.2 800 54.0 900 52.0 1000 47.51100 40.0 1200 34.5

From the foregoing data, typical of the invention it will be observedthat the desired hardness and graphite levels as well as uniformity ofhardness across the section are attained. The data show, furthermore,that the steels are satisfactorily resistant to tempering.

According to the provisions of the patent statutes, I have explained theprinciple of my invention and have described what I now consider torepresent its best embodiment. However, I desire to have it understoodthat, within the scope of the appended claims, the invention may bepracticed otherwise than as specifically described.

I claim:

1. A hot worked and heat treated article of manufacture formed fromsteel containing about 1 to 2 percent of carbon, not over about 0.2percent of chromium, about 1.7 to 2.5 percent of manganese, about 1.3 to1.75 percent of molybdenum, about 1 to 2.5 percent of nickel, about 1 to1.5 percent of silicon, and the remainder iron together with elementsand impurities in amounts that do not adversely affect the hardening andgraphitizing properties, said article having spheroidized carbides andat least about 0.2 percent of graphitic carbon substantially uniformlydistributed throughout its section, and having a hardness of at leastRockwell C 58 throughout sections at least as great as six inchesdiameter resulting from cooling in air from an austenitizingtemperature.

2. A hot worked and heat treated article of manufacture according toclaim 1 containing about 1.35 percent of carbon, less than about 0.15percent of chromium, about 1.85 percent of manganese, about 1.4 to 1.6percent of molybdenum, about 1.8 to 1.9 percent of nickel, and about1.15 to 1.25 percent of silicon.

3. Steel containing about 1.35 percent of carbon, less than about 0.15percent of chromium, about 1.85 percent of manganese, about 1.4 to 1.6percent of molybdenum, about 1.8 to 1.9 percent of nickel, and about1.15 to 1.25 percent of silicon, and the remainder iron together withelements and impurities in amounts that do not adversely affect thehardenability and graphitizing properties, said steel beingcharacterized by capability of being hot worked and upon cooling in airfrom an austenitizing temperature of producing structures ofspheroidized carbides with at least about 0.2 percent of graphiticcarbon substantially uniformly distributed throughout its section, andhaving a hardness of at least Rockwell C 58 throughout sections at leastas great as six inches diameter.

References Cited in the file of this patent UNITED STATES PATENTS1,910,034 Mitchell et al. May 23, 1933 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No, 2,883,281 April 21, 1959 Chester F.Jatczak It is hereby certified that error appears in the-printedspecification of the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 4, line 18, in the table, second column thereof, opposite "300, I

Signed and sealed this: 30th day of June 1959.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Ofliccr Commissioner ofPatents

3. STEEL CONTAINING ABOUT 1.35 PERCENT OF CARBON, LESS THAN ABOUT 0.15PERCENT OF CHROMIUM, ABOUT 1.85 PERCENT OF MANGANESE, ABOUT 1.4 TO 1.6PERCENT OF MOLYBDENUM, ABOUT 1.8 TO 1.9 PERCENT OF NICKEL, AND ABOUT1.15 TO 1.25 PERCENT OF SILICON, AND THE REMAINDER IRON TOGETHER WITHELEMENTS AND IMPURITIES IN AMOUNTS THAT DO NOT ADVERSELY AFFECT THEHARDENABILITY AND GRAPHITIZING PROPERTIES, SAID STEEL BEINGCHARACTERIZED BY CAPABILITY OF BEING HOT WORKED AND UPON COOLING IN AIRFROM AN AUSTENITIZING TEMPERATURE OF PRODUCING STRUCTURES OFSPHEROIDIZED CARBIDES WITH AT LEAST ABOUT 0.2 PERCENT OF GRAPHITICCARBON SUBSTANTIALLY UNIFORMLY DISTRIBUTED THROUGHOUT ITS SECTION, ANDHAVING A HARDNESS OF AT LEAST ROCKWELL C 58 THROUGHOUT SECTION AT LEASTAS GREAT AS SIX INCHES DIAMETER.